One of the things I've observed with malignant personalities is that they seem to sense when you've caught on to their act. This is also the point at which they begin to avoid you. Whether it's because they're uncomfortable facing you, or they're worried you possess enough information to expose them, or they're no longer getting their narcissistic "supply" from you, they no longer want to be in your presence.
If you've known a narcissistic individual for a while, and she's selected you as a target, the discovery of her disordered personality usually comes at the end of the relationship. That's when she decides you no longer serve her purpose, and she is ready to discard you. Typically, this is done in a cruel and humiliating manner. If you had a "friendship" with this person, you can consider her actions a betrayal, because she had previously gained your trust and probably access to your secrets as well. It's this insider information that served her well, as she plotted ways to bring you down.
It would be a rare narcissist who didn't wage a smear campaign at this point, as she attempts to assassinate your character and turn you into a social outcast. Actually, according to the typical pattern of narcissistic abuse, the false rumors probably started much earlier, months, or even longer, before you realized you had an emotion predator in your life.
It's been a few years since a female malignant narcissist "frenemy" left my side. During this experience, I learned a few things about these dark souls who often hide behind a mask of piety. Perhaps the best advice I can give is to read up on this all-too-prevalent disorder, so you clearly understand what to look for when meeting a new person for the first time.
In the aftermath of my narcissistic encounter, I met other women who seemed to fit the criteria. This I could sense right away. The strange thing is that they also seemed to know that I knew that their carefully polished exterior was fake. The fact that I knew this appeared to frighten them so much that they didn't try to bother me.
There is a saying that "knowledge is power." This is very true when dealing with a malignant narcissist.